MMU Notifiers and the quest for graphics feature parity

[René Ladan]

2016-05-12 5:37 GMT+02:00 K. Macy <kmacy at freebsd.org>:
> My motivation for writing this email stems from my recent work extending the
> linuxkpi to facilitate updating graphics support for FreeBSD. I've made
> reasonable progress limiting my changes to the linuxkpi so far. I have 3D HW
> acceleration working on an essentially unmodified 4.6-rc5 drm and i915 driver.
> The 4.6 i915 driver supports all of Haswell (3.8 doesn't), Broadwall, Skylake,
> and the, as of yet, unreleased Kaby Lake processors. Additionally, I am
> expecting a Thinkpad e565 (AMD based) to arrive on Friday which will allow me
> to bring up amdgpu (the Radeon driver for post 2013 AMD GPU hardware) this
> weekend. I find this exciting as it means that FreeBSD will be able to run on
> _all_ x86 graphics hardware. Unfortunately, most if not all ARM GPU drivers
> are closed source.
>
> This isn't quite everything though. There is a new "userptr" ioctl in
> graphics drivers that allows applications to safely register user memory with
> the driver. This works because  if pages are evicted or the process goes away,
> the driver will be notified first. This notification takes place through the
> "mmu notifier" facility.
>
> MMU Notifiers are essentially just VM callbacks (or in FreeBSD parlance
> eventhandlers). They were first added to Linux to enable KVM to better
> interoperate with the native VM's resident set management:
>
> https://lwn.net/Articles/266320/
>
> They're now also used by IB, IOMMUs, MPSS (Xeon Phi), and graphics drivers.
> The API is well enough documented in the header file:
>
> http://lxr.free-electrons.com/source/include/linux/mmu_notifier.h
>
>
> I don't have strong feelings for what these are called or their precise
> location. I do, however, need to be able to support roughly equivalent
> semantics when I register these eventhandlers from the notifer calls in the
> linuxkpi.
>
> I haven't worked on the VM in a year or two so don't know quite how to proceed.
> I'm happy to produce patches for review, but fear that they might be rejected
> out of hand for one reason or another. I'd like feedback on the approach
> itself and what I might do to make any proposed patches more palatable.
>
I have a laptop with both an nVidia GeForce 940M and a built-in
graphics card on the Intel i7 6500U CPU:
vgapci0 at pci0:0:2:0:     class=0x030000 card=0x09851025 chip=0x19168086
rev=0x07 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'HD Graphics 520'
    class      = display
    subclass   = VGA

So if I understand correctly this 520 chip might work with your patch?
Stock FreeBSD 11.0 r298793 with xf86-video-intel 2.21.15_9 does not
see the driver.
For now it does run with scfb.

Thanks for your work,
René
-- 
https://rene-ladan.nl/